Water tube steam generator



Sept. 11, 1951 R. s. cox 7,

WATER TUBE STEAM GENERATOR Filed May 28, 1947 4 Sheets-Sheet 1 ySCox w w. 2 W

INVENTOR fiodne BY ATTORN EY iii/27721 Sept. 1951 R. s. cox 2,567,695

WATER TUBE STEAM GENERATOR Filed May 28, 1947 4 Sheets-Sheet 2 INVENTOR .Poaneg J Cox M0019 ATTORNEY Sept. 11 1951 s, (:Q)( 2,567,695

Filed May 28, 1947 4 Sheets-Sheet 5 NNNNNN OR ATTORNEY Sept. 11, 1951 R. s. cox

WATER TUBE STEAM GENERATOR 4 Sheets-Sheet 4 Filed May 28, 1947 INVENTOR .Poan BY ey 5T Cox ATTORNEY Patented Sept. 11, 1951 UNITED STATES PATENT OFFICE WATER TUBE STEAM GENERATOR Rodney S. Cox, Marion, Ohio, assignor to The Babcock & Wilcox Company, Rockleigh, N. J., a corporation of New Jersey Application May 28, 1947, Serial N0. 751,109

16 Claims.

This invention relates to improvements in steam generators of the water tube type.

The invention is specifically concerned with a high duty steam generator of the water tube type in which the fluid circuit involves a central downcomer improving circulatory conditions by presenting a minimum of flow restrictions, the central downcomer being integrated with a lower water chamber and an upper water chamber to which a multiplicity of relatively small diameter steam generating tubes are connected in the circulation system.

' An object of the invention is to provide a water tube steam generator of the above indicated type which effectively utilizes a minimum of space with a lowratio of external setting wall area to steam generating capacity.

Further objects of the invention include the provision of a steam generator which has a separately fired superheater furnace. whereby superhea't temperature control may be efiected by independent firing of the furnaces one of which develops gases for the generation of saturated steam and the other develops gases primarily for superheatin'g.

The invention also involves a water tube steam generator having a unitary pressure vessel serving as the non-heated portion of a natural circulation steam generating circuit and also acting as a rigid central support for the tubular elements which are annularly arranged about the central support.

A further object of the invention is to provide a high duty water tube steam generator having steam generating surfaces presented by spaced tubes. extendin transversely of gas flow, the arrangement being such that the gas flow path is in the nature of a circular annulus to which heating gases are supplied from an integrated combus-tion chamber, the gas pass and combustion chamber being enclosed within a substantially cylindrical setting.

Another object of the invention is to provide a water tube steam generator of the above indicated type, so constructed and arranged within a compact and generally cylindrical casing that it incorporates efiicient steam generating surfaces and efficient tubular superheating surfaces for delivery of superheated steam from the combined unit.

The invention is particularly concerned with a water tube steam generator which is characterized by high rates of heat transfer rather than high rates of steam delivery or capacity. High heat transfer rates are promoted by the flow of 2 gases across the component tubular heating elemerits.

The steam generator of the invention is also characterized by low draft loss and by a low ratio of external casing area to heating gas pass volume. By utilizing direct connection of steam generating tubes to a central pressure vessel, the steam generator minimizes the weight and cost of such construction, and the arrangement of vertically extending radial rows of steam generating tubes directly connected to the central pressure vessel provides highly effective heatti'ansfer surfaces which are radially supplied. with water from the lower submerged chamber, and radially Vented to the upper steam and water chamber.

The steam generator of the invention also contributes to high duty characteristics in that tubular heat absorbing surfaces of different optimum diameters may be utilized at different positions in the annular heating gas flow path, in accordance with the heating *gas properties at such positions.

The steam generator of the vention will be described with reference to the accompanying drawings which illustrate preferred embodiments of the invention, and other objects of the inven tion will appear as the description proceeds.

In the drawings:

Fig. 1 is a vertical section on the multiple plane section lines indicated at l--l 'of Fig. 2; v

Fig. 2 is a horizontal section taken on the section line 2-2 of Fig. 1;

Fig. 3 is a vertical section on the section line 3-3 of Fig.2;

Fig. 4 is a vertical section of modified form of the illustrative steam generators on line 4-4 of Fig. 5;

Fig. 5 is a horizontal section through the Fig. 4 modification showing some of the steam generating tubes in partial elevation; and

Fig. 6 is a horizontal section of the'Fig. 4 modification on the line 6-6 of Fig. 4.

The illustrative steam-generator includes a central pressure vessel the upper part of which is preferably of spherical shape and constitutes the steam and water drum Ill.- The lower part of this pressure vessel is similar in shape and constitutes a submerged chamber [2. The chambers l0 and l 2 are connected by a tubular mid-section [4 which constitutes the downcomer of the circulatory system of the steam generator. 1

The exterior wall of the 'installation is formed by substantially upright cylindrical icasing 16, which encloses'a bank of uprightsteam -generatin tubes 18. These tubes, as clearly -i-i'idicated in the drawings, have their lower ends connected to the submerged chamber I2 so that, in normal operation, they receive water therefrom. Their upper ends are connected to the steam and water chamber I0, and the tubes of this bank are arranged somewhat in annular form about the central downcomer I4 of, the pressure vessel construction.

The radial spacing of the steam generating tubes of the convection steam generating bank is uniform throughout the major or upright portions of the tubes, while the divergence of rows varies the row to row spacing, dependent upon the transverse or radial position in the gas pass. This row to row spacing equalizes the transverse distribution of gas flow through the bank of tubes.

The illustrative steam generator is fired b the burners 20-42 which are arranged for tangential firing. As clearly indicated in Fig. 2 the furnace 24 has a Wall 23 which is tangential with respect to 'theremainder' of the casing IB'and it is lined with steam generating wall cooling tubes 28 appropriately connected into the boiler circulation. Preferably these tubes have metallic extensions welded thereto over their faces exposed to the heat from the furnace gases. The furnace face of this "wall of extended surface tubes is formed by a covering of ceramic refractory material 30. The opposite wall of the furnace or combustion chamber 24 is similarly constructed of wall cooling'stud tubes 32 and ceramic refractory material 34, all arranged to form a wall which is substantially radial to the installation, leading inwardly from the casing at the position 36 to contact with the downcomer I4.

A circular fluid cooled wall of similar stud and refractory construction is indicated at 33. This Wall'includes the innermost tubes of the radial rows of steam generating tubes I8, and it extends from the upper steam and water chamber II] to the water chamber I2 so as to protect the downcomer or intermediate conduit I4 from contact with the high temperature furnace gases.

The furnace gases pass over the steam generating tubes and then'over tubes of a superheater 42. From the superheater the gases pass in a generally circular path over the remainder of the steam generating tubes to the economizer 44. The economizer includes an upright inlet header 46 which is suitably connected to a source of feed water. It also includes a similarly positioned outlet header 48 spaced circumferentially of the casing from the inlet header, as indicated in Fig. 2. The headers 48 and 48 are connected by a plurality of return bend tubes such as that shown at 50 in Fig. 2. These return bend tubes are also indicated in Fig. 3 as being spaced vertically, the lowermost tube being indicated at 52. From the economizer the gases pass upwardly and out of the installation through the flue 54 (indicated in dot and dash lines in Fig. 2)

The superheater, indicated generally in Fig. 2 at 42, has a unitary header construction 56 with an inlet header section 58 and outlet header section 60 separated b a horizontal diaphragm 62. The inletheader section is connected by the conduit 64 with the steam and water chamber Iii.

Saturated steam from the steam and water chamber In flows through the conduit 64 and through the superheaterheader inlet section 58 to a plurality of rows of upright tubes III which have their inlets directly communicating with section 58. The steam is conducted by these tubes to .an intermediate header l' which is disposed below the casing I6, as indicated in Fig. 3 From the header I2 the steam flows upwardly through the tubes I4 to the outlet header section 60 and thence through a conduit I6 to a position of use.

The modified steam generator construction shown in Figs. 4, 5, and 6 includes the upper steam and water drum connected to the submerged drum 92 by large diameter downcomer 94. The steam generator is inclosed in the upright casing 96 between which and the drums there are steam generating tubes as indicated by the banks of .tubes 91 and 98 in Fig. 4. These tubes are disposed in rows extending outwardly from the submerged drum 92 and from the upper drum 90, their intermediate parts being vertically arranged in the generally transverse path of the heating gases. The rows of the bank 98 are substantially radially arranged relative to the downcomer 94. this arrangement having an equalizing influence on the gas flow through the bank.

The heating gases are provided by the tangentially arranged burners such as those indicated at I90 and I02 in Figs. 5 and 6. The gases from the burner I90 are directed substantially tangentially between the casing and the inner pressure vessel construction by inner and outer walls I84 and I09 which are formed by some of the steam generating tubes, with ceramic refractory material disposed in the spaces between the tubes. Immediately confronting the burner I00 and within the steam generator casing are three rows IiQ-HZ of screen tubes (of the bank 91) disposed so as to protect the tubes H4 and N6 of a superheater indicated as an entiret by II3 (Fig. 5). The superheater may receive steam from the steam and water drum 90 through appropriate headers and tubular connections.

The steam generating tubes of the bank 98 are arranged in radial rows such as those indicated at I24-I2'I, inc. in Fig. 6. The largediameter tubes of the rows I22 and I23 constitute a tubular screen directly confronting the burner I02. The gases, after passing over the steam generating tubes, pass upwardly to the flue I 20.

Forwardly of the row of tubes I22, there is the combustion chamber I30, the opposite sides of which are formed by fluid cooled walls such as I32 and I34 (Fig. 6) formed by upright steam generating tubes with the spaces between the tubes closed by-a ceramic refractory material.

The arrangement of tubes leading from the lower drum 92 to the wall I34 is indicated by the upper right hand part of Fig. 5 of the drawing wherein the tube sections such as I40-I43 lead from the submerged drum 92 as floor tubes to positions along the wall I34. The intermediate sections of these' tubes extend past the combustion chamber I30 and the upper parts of the same steam generating tubes may have a similar arrangement (similar to the arrangement of the floor tubes shown in Fig. 5) by which the tubes are disposed for connection of their upper parts with the steam and water drum 9!).

Either of the steam generating units'described above may be eifectivelysupported by means associated directly with the central pressure vessel construction which provides a steam and water drum, a submerged drum, and the connecting downcomer. The entire unit may thus be conveniently top supported by tension means, or it may be radially bottom supported.

The illustrative steam generating units are also characterized by minimum changes in. the direction of the products of combustion as they enter the convection heat absorbing sections. The minimum change of direction here referred to is that Which'relates to the direction of burner delivery of the combustion products.

It is also to be taken intoconsid'eration that the illustrative steam generating units utilize fluid fuel burners of a high capacity type which handle a large volume of combustion air, under pressure. In the operation of the units, the combustion air under pressure, and possible pre-,.

heated-When anair heater is utilized beyond the uptake connection, is delivered to the fluid fuel burner casing, and the furnace, because of its cylindrical form may be effectively operated at superatmospheric pressure, a the result of air delivery pressure sufficient toovercometh flow resistance of the heat absorbing-surfaces.

In the embodiment of the invention indicated in Figs. 4'and '6, the two fuel burners are positioned at substantially the same elevation in the lower portion of their respective combustion chambers, and the heating gases leaving the superhea'ter -I I3 and, pas-sing through the unrestricted space rearwardlyof the superheater, rise over the wall I32 and pass through the double tube screen into the furnace use. This tube 'screen'is formed by the'rows of upright tubes ['50 and I 52 which are appropriately connected 'into the fluid circulation of the unit. This gasflOW is restricted to the upper portion of the furnace I39 above the fuel and air delivery components of the burner H372 by the wall 132 (formed by the lowerparts-oi' the tubes I50 and 452, with refractory mate-rial closing theintertube spaces) so that the gases coming from the superheater furnace i 53 will not interfere with the combustion (fuel and air delivery) by the burner The gases flowing through the combustion chamber 136 will then consist of an upper stream from 1*.

the superheater furnace 1'53 and a lower stream from the burner 152. "The upper stream will be at a temperature lower than the temperature of the gases of the lower stream due to the heat absorbed by the surfac encountered by the gases from the superheater furnace. Subsequent flow of the gases through the closely spaced small diameter tubes of the convection bank 93 will tend to equalize gas temperatures.

Fig. 6 of the drawings shows an inner wall 158 similar to the wall -33 of the Fig. 3 installation and including the upright steam generating tubes I62 arranged in a circular row. These tubes are provided with metallic studs welded thereto and extending into inter-tube spaces, the studs and the tub-es being covered with refractory mate- :rial. This wall I60 may be extended so as to complete the circular arrangement of the wall by using the innermost tube of every third radial row of such rows "of tubes as indicated at 125, I25, and 126. In this cas the innermost tubes are so closely arranged that they are not provided with studs or intervening refractory. This leaves two-thirds of the rows of tubes of the bank 58, of shorter radial extent so that, in the main portion of the annulus, a relatively close spacing of the vertical tube is efiiected.

What is claimed is:

1. In a steam generator, a unitary pressure vessel including an upright :tubular downcomer connecting an upper steam and water chamber and a lower water chamber, an upright exterior wall circumscribing said pressure vessel and spaced radially therefrom to provide space for high temperature heating gases, upright steam generating tubes exposed to the heating of the furnace gases in said space, said tubes having their upper ends in connection with the steam and Water chamber and their lower ends in communication with the lower water chamber, a fuel burner arranged for tangential firing relative to-said wall for producing high temperature gases for heat exchange in the installation, a flue for the exit of furnace gases beyond the steam generating surface, said flue being constructed and arranged to cause the gases :to arcuately traverse said space, an economizer including spaced convection heating tubesexpo'sed to the heat of furnace gases at a position beyond the steam generating tubes relative to gas flow, a connection between the outlet of the economizer and said pressure vessel, and a superheater including spaced convection heating tubes disposed beyond at least some of said steam generating tubes relative to gas flow.

2. In a steam generator, a unitary upright pressure vessel having a steam and water chamber at its upper end and a submerged water chamber at its lower end, said pressure vessel also having an intermediate section of a large diameter constituting the downcomer for the steam generator, a casing circumscribing the pressure vessel and radially spaced therefrom, steam generating tubes directly connecting the water chamber to the steam and Water chamber and disposed in and annularly arranged within the casing and about the downcomer, a first burner arranged to fire substantially tangentially with reference to the casing to produce furnace gases for heating the steam generating tubes, a superheater having tubes disposed Within the casing, a second tangentially arranged burner for separately heating the superheater, and means 'forming an outlet for the gases which have passed over the superheater.

3. A water tube steam generator comprising a unitary assembly of tubular members including a central upright pressure vessel and a plurality of radially extending rows of steam generating tubes having their lower and upper ends connected respectively to the corresponding lower and upper portions of said vessel, each row comprising a multiplicity of upright tubes, a heating gas confining casing positioned about the outer tubes of said rows as well as above and below the tubes of said rows and extending annularly of said tube rows and said vessel, means introduc- 'ing heating gases to said casing, said means including a burner and a combustion chamber disposed laterally of said tubes and at a level between the upper and lower ends of said tubes, mean-s forming a gas outlet port limited to a position substantially 'circumferentially spaced from said means and disposed on the side of said rows of tubes opposite said heating gas introducing means whereby cross-tube flow of gases over the tubes of said rows and circumferentially of the pressure vessel is accomplished and an upright wall extending outwardly from a position adjacent the pressure vessel to the casing and disposed between the gas outlet port and the gas introducing means.

4. A water tube steam generator comprising a unitary assembly of tubular members including a central upright pressure vessel and a plurality of radially extending rows of steam generating tubes forming a bank of tubes having their lower and upper ends connected respectively to the lower and upper portions of said vessel, a heating gas confining casing positioned about the outer tubes of said rows as well as above and below the tubes and extending annularly of said tube rows and said vessel, means introducing heating gases into said casing, a superheater including a bank of spaced tubes disposed across the gas flow at a position between some of said radial rows of tubes, means forming a gas outlet port limited to a position substantially circumferentially spaced from said gas introducing means and dis posed on the side of said rows of tubes opposite said heating gas introducing means whereby cross-tube flow of gases over the steam generating tubes and the superheater tubes is accomplished, the superheater and the steam generating tubes being operatively disposed intermediate said means and the gas outlet part circumferentially of said pressure vessel, and an upright wall extending outwardly from a position adjacent the pressure vessel to the casing and dis posed between the gas outlet port and the gas introducing means.

5. A water tube steam generator comprising a unitary assembly of tubular members including a central upright pressure vessel and a plurality of radially extending rows of steam generating tubes having their lower and upper ends connected to the respective portions of said vessel, a heating gas confining casing positioned about the outer tubes of said rows as well as above and below the tubes of said rows and extending annularly of said tube rows and said vessel, a first means introducing heating gases to said casing, a superheater including a bank of spaced tubes disposed at a position intermediate said radial rows of tubes, a gas outlet port circumferentially spaced from said means whereby cross-tube flow of gases over the tubes of said rows is accomplished, a second heating gas introducing means functioning to heat the superheater, and a wall including a row of steam generating tubes positioned within said casing between said gas outlet port and said second heating gas introducing means, said wall extending from a position adjacent the pressure vessel to the casing.

6. A water tube steam generator comprising a unitary assembly of tubular members including a central upright pressure vessel and a plurality of radially extending rows of steam generating tubes having their lower and upper ends connected to the respective portions of said vessel, a

heating gas confining casing positioned about the outer tubes of said rows as Well as above and below the tubes of said rows and extending annularly of said tube rows and said vessel, means forming a combustion chamber within the casing,

a fuel burner directing combustion constituents into the combustion chamber, means forming a gas outlet port circumferentially spaced from said first means whereby cross-tube flow of gases over the tubes of said rows is accomplished, and a multiple tube economizer having tube sections extending across the gas flow and disposed between said gas outlet port and a radial row of said steam generating tubes remote from the fuel burner.

7. A water tube steam generator comprising a unitary assembly of tubular members including a central upright pressure vessel and a plurality of rows of steam generating tubes having their lower and upper ends connected to the respective portions of said vessel, said rows of tubes extending outwardly from the pressure vessel, a heating gas confining casing positioned about the outer tubes of said rows as well as above and below the tubes of said rows and extending annularly of said tube rows and said vessel, means forming a combustion chamber disposed within the casing and laterally of said tubes, a fuel burner directing combustion constituents into the combustion chamber, means forming a gas outlet port circumferentially spaced from the combustion chamber with said rows of tubes being interposed relative to the combustion chamber and the flue whereby cross-tube flow of gases over the tubes of said rows is accomplished, and a wall extending outwardly from a position adjacent the pressure vessel to said casing at a position between the outlet port and the fuel burner.

8. In a water tube steam generator, a centrally disposed pressure vessel including an upper portion constituting a steam and water chamber and a lower portion constituting a submerged water chamber, said pressure vessel also including an upright tubular downcomer integral with said chambers and directly connecting them, a substantially cylindrical upright casing radially spaced from said pressure vessel to provide heating gas spaces therebetween, spaced upright steam generating tubes subjected to the heat of furnace gases within said space and having their upper and lower endsconnected to said upper and lower chambers respectively, circumferentially spaced first and second fuel burners disposed near the lower part of said generator, some of said steam generating tubes being disposed so as to form circumferentially spaced first and second combustion chambers for the respective fuel burners, others of said steam generating tubes being disposed as tubular screens across the outlets of said combustion chambers, a superheater including spaced upright tubes disposed across the gas flow rearwardly of said first combustion chamber and between that combustion chamber and the second combustion chamber, and means forming a heating gas outlet port disposed near the upper end of the generator, some of the tubes along a boundary of the second combustion chamber defining a wall constructed and arranged to prevent gases from the superheater combustion chamber from passing directly into the space at the level of the burner for the second combustion chamber but spaced apart at a higher level to permit the gases from the first combustion chamber to join the gas-es from the second combustion chamber in passing across steam generating tubes disposed between the second combustion chamber and said gas outlet port.

9. In a Water tube steam generator, a centrally disposed pressure vessel including an upper portion constituting a steam and water chamber and a lower portion constituting a submerged water chamber, said pressure vessel also including an upright tubular downcomer integral with said chambers and directly connecting them, a substantially cylindrical upright casing radially spaced from said pressure vessel to provide heating gas spaces therebetween, spaced upright steam generating tubes subjected to the heat of furnace gases within said space and having their upper and lower ends connected to said upper and lower chambers respectively, circumferentially spaced first and second fuel burners disposed near the lower part of said generator, some of said steam generating tubes being disposed so as to form circumferentially spaced first and second combustion chambers for the respective fuel burners, others of said steam generating tubes being disposed as tubular screens across the outlets of said combustion chambers, a superheater including spaced upright tubes disposed across the gas flow rearwardly of said first combustion chamber and between that combustion chamber and the second combustion chamber, and a heating gas outlet port disposed near the upper end of the generator, some of the tubes along a boundary of the second combustion chamber defining awall constructed; and arranged as a substantially gas, tight wall at the burner level to prevent gases. from the superheater combustion chamber from passing directly into the space in front of the burner for the second combustion chamber and spaced apart to form a tubular screen above said burner level to permit the gases from the superheater combustion chamber to join the gases from the secondcombustion chamber in passing across steam generating tubes disposed between the second combustion chamber and said gas outlet port.

10. In a steam generator, a unitary upright pressure vessel having a steam and water chamber at its upper part and a submerged water chamber at its lower part, said pressure vessel also having a tubular intermediate section of large diameter constituting the downcomer for the steam generator, a casing circumscribing the pressure vessel and radially spaced therefrom, upright steam generating tubes directly connecting the water chamber to the steam and water chamber. and disposed in and annularly arranged within the casing about the downcomer, a coma;

busti'on chamber leading toward the steam generating tubes, a burner directing burning fuel into the combustion chamber and substantially tangentially of the casing to produce furnace gases for passing over the steam generating tubes and around the downcomer, a superheater having tubes disposed within the casing at a position beyond the first of the steam generating tubes relative to gas flow, an economizer having tubes disposed within the casing beyond steam generating tubes, and a gas flue adjacent the economizer. ,11. Ina water tube steam generator, a central pressure vessel including an upper steam and water chamber of circular transverse section, a lower water chamber of circular transverse section spaced from said upper chamber, a large diameter downcomer connecting the upper and lower chambers and in upright axial alignment therewith, a substantially cylindrical casing or upright wall extending between said chambers and defining an annular space around the pressure vessel, a bank of steam generating tubes comprising a plurality of circumferentially spaced radially arranged rows of spaced upright tubes having their lower ends connected to said lower chamber and their upper ends connected to said upper chamber, said bank of tubes extending substantially concentrically of said central vessel over a portion of its circumference and substantially filling a segment of the annular space between the pressure vessel and the casing, the steam generating tubes being so spaced radially in the radial rows that the horizontal spacing of the tubes over an arcuate zone near the downcomer is smaller than in an arcuate zone remote from the downcomer, said casing or upright wall being radially spaced from said central vessel and circumscribing the space containing said bank of tubes and a combustion chamber circumferentially adjacent said bank, fuel burner means associated with said combustion chamber, and means forming a gas outlet circumferentially remote from the fuel burner means, said fuel burner means being disposed laterally of the casing and said tubes and at a level above the lower end of the pressure vessel.

12. In a vapor generator, an upright pressure vessel including an upper part constituting a vapor and liquid chamber and a lower part constituting a liquid chamber, the intermediate part of' the pressure vessel constituting an upright tubular downcomer connecting said chambers, upright vapor generating tubes connecting said chambers, an upright casing circumscribing and enclosing the pressure vessel and said tubes, said casing being substantially radiallyspaced from the downcomer so as to provide a circumferential heating gas space therebetween, a wall extend:- ing outwardly from a position adjacent the pressure vessel tothe casing, furnace gas. supplying means associated-with the casing at one side of said wall and'directing furnace gases into said space, means forming a furnace gas outlet communicating with said space at the other side of said Wall so that the gases from said first means pass circuinferentially around the pressure vessel and over said tubes to said-outlet. 3

13. In a vapor generator, an upright pressure vessel including an upper part constituting a vapor and liquid chamber and a lower part co'nsti' tuting a liquid chamber, the intermediate part of the pressure vessel constituting an upright tubular downcomer; connecting said chambers,

:upright vapor. generating tubes connecting said chambers, an upright casing circumscribing and enclosing the pressure vessel and said tubes, said casingbeing substantially radially spaced" from the downcomer so as to provide a circumferential heating gas space therebetween, a wall extending outwardly from a position adjacent the pressure vessel to the casing, furnace gas supplying means associated with the casing at one side of said wall and directing furnace gases into said space, means forming a furnace gas outlet communicating with said space at the other side of said wall so that the gases from said first means pass circumferentially of the pressure vessel and over some of said tubes to said outlet, a combustion chamber associated with the casing at a position intermediate the path of gas travel, and a superheater disposed between said furnace gas supply means and the combustion chamber, the effect of said gas supplying means being variable to maintain a constant superheat.

14. In a vapor generator, an upright pressure vessel including an upper part constituting a vapor and liquid chamber and a lower part constituting a liquid chamber, the intermediate part of the pressure vessel constituting an upright downcomer connecting said chamber parts, upright vapor generating tubes connecting said chambers, an upright casing circumscribing and enclosing the pressure vessel and said tubes, said casing being substantially radially spaced from the downcomer so as to provide a circumferential heating gas space therebetween, a wall extending outwardly from a position adjacent the pressure vessel to the casing, furnace gas supplying means associated with the casing at one side of said wall and directing fur nace gases into said space, means forming a furnace gas out-let communicating with said space at the other side of said wall so that the gases from said first means pass circumferentially of the pressure vessel and over some of said tubes to said outlet, a combustion chamber associated with the casing at a position intermediate the path of gas travel, and a superheater disposed between said furnace gas supply means and the combustion chamber, parts of some of said tubes being spaced apart and presenting a tubular screen between the superheater and said gas supplying means to permit gases to pass from said means through the combustion chamber and thence to said outlet.

-'piesure vessel pitiviiii-iig upper and lower liquid chambers, horizontally spaced upright vapor generating tubes directly connecting said chambers and disposed circumferentially of the pressure Vessel, a casing EcircumferentiaIIy enclosing said tubes, an uprightwall extending from a position adjacent the pressure vessel to the casing, means forming a furnace gas outlet on one side of said wall, a first combustion chamber from which furnace gases pass over some of said tubes to said outlet, a superhater including tubes dispbsed between said combustion chamber and said wall, and a second combustion chamber disposed between the superheater and said wall.

I 16. In a vapor, generator, an upright central structure including an upper vapor and liquid chamber and a' lower liquid chamber connected b9 dbwhcome'r means, horizontally spaced upright vapor generatingv tubes directly connecting said chambers and disposed circumferentially of the central structure; an upright casing circumferentially enclosing the tubes and the central structure and providing a circumferential gas pass around the central structure, an upright Wall extending from a position adjacent the central structure to the casing, means forming a furnace 12 gas outlet limited to a position at one side of said wall, furnace gas introducing means at the other side of said wall, said furnace gas introducing means projecting fuel and air into the inlet of the circumferential gas pass and in a direction transversely related to the upright tubes within the gas 'pass.

RODNEY S. COX;

REFERENCES CITED The following references are (if record in the file er this patent UNITED STATE fATENTS Number Name Date 1,339 DeWitt Sept. 25, 1839 26,788 Schaubel Jan. 10, 1860 262,392 Foster Aug. 8, 1882 372,346 Walters Nov. 1, 1887 2,044,270 Wood June 16, 1936 2,100,190 Jackson Novj 23, 1937 2,216,117 Krug Oct. 1, 1940 2,231,015 Lucke Feb. 11, 1941 2,271,880 Wood Feb. 3, 1942 2,327,161 Badenhausen Aug. 17, 1943 2,332,508 Daniels Oct, 26, 1943 

